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DIELECTRIC MEASUREMENTS OF FIVE DIFFERENT

SOIL TEXTURAL TYPES AS FUNCTIONS OF

FREQUENCY AND MOISTURE CONTENT

Ramon L. Jesch

Electromagnetic Fields Division

Center for Electronics and Electrical Engineering

National Bureau of Standards

Boulder, Colorado 80303

October 1978

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DIELECTRIC MEASUREMENTS OF FIVE DIFFERENT

SOIL TEXTURAL TYPES AS FUNCTIONS OF '''I

FREQUENCY AND MOISTURE CONTENT

Ramon L. Jesch

Electromagnetic Fields Division

Center for Electronics and Electrical Engineering

National Bureau of Standards

Boulder, Colorado 80303

October 1978

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

CONTENTS

Page

1 . INTRODUCTION 1

2. MEASUREMENT APPARATUS AND THEORY 1 2.1 Background 1 2.2 Sample Holders 1 2.3 Theory of Electromagnetic Properties Determination 3 2.3.1 Center Conductor Correction For Electric Field Extension 4

3. MEASUREMENT APPROACH 5 3.1 Measurement System 5 3.2 Sample Preparation 5 3.2.1 Soil Texture Construction 5

4. EXPERIMENTAL RESULTS 7

5. DATA SUMMARY 22

6. CONCLUSIONS 22

7. ACKNOWLEDGMENT 22

8. REFERENCES 22

iii

DIELECTRIC MEASUREMENTS OF FIVE DIFFERENT SOIL TEXTURAL

TYPES AS FUNCTIONS OF FREQUENCY AND MOISTURE CONTENT

Ramon L. Jesch

Open-circuit coaxial transmission-line sample holders were used to determine the electromagnetic dielectric properties of five soil textural

types as functions of moisture level content and frequency. A brief outline of the theoretical basis is given for the open-circuit method along

with the measurement system and the sample preparation. Experimental

results are given for the different soil textural types for moisture

levels ranging from 0 to 48 percent and for test frequencies ranging

from 300 to 9300 MHz.

Key words: Attenuation; coaxial sample holder; density; dielectric

properties; relative dielectric constant; soil textural types.

1. INTRODUCTION

This final report covers the results of measurements that were made on five soil textural

types that included sand, sandy loam, silt loam, clay loam, and clay to determine their electromagnetic properties of permittivity (dielectric and attenuation constants) as functions

of frequency and moisture content. The soils were prepared and furnished by Robert Falls of

the U.S. Army Mobility Equipment Research and Development Center (MERDC) at Fort Belvoir,

Virginia. The calculations were made from measurements of the propagation characteristics

of 14 mm open-circuit coaxial transmission-line sample holders that were filled with the

different soil types. The measurements were taken at test frequencies of 300, 500, 1000,

2000, 4000, and 9300 MHz for moisture levels ranging from 0 to 48 percent (of dry soil weight)

.

2. MEASUREMENT APPARATUS AND THEORY

2 . 1 Background

Transmission-line measurements of a dielectric sample terminated by either a short

circuit or an open circuit are well known [1]. The coaxial open-circuit method used in the

present work had been previously developed for measurements of lunar soil [2] and various

grains [3] over wide frequency ranges. The open circuit has the advantage that the sample

is easily inserted through the open end and that the results maintain essentially constant

accuracy particularly at low frequencies. On the other hand, an offset coaxial short

circuit can exhibit unacceptable errors at frequencies below 500 MHz. The sections below

give a brief outline of the theoretical basis for the open-circuit method and are based on

the theoretical development in reference [3].

2.2 Sample Holders

The measurement apparatus consists of open-circuit coaxial sample holders of the design

illustrated in figure 1. The sample holders (fig. 2) were fabricated from 14 mm 50-ohm

precision coaxial air-line stock and equipped with the type 900-BT precision coaxial connector assembly. The design allows the outer conductor to be unscrewed at the plane of the bead

interface between sections 1 and 2 —thus, allowing easy soil sample removal. A flat-faced

teflon bead was used in place of the regular undercut connector bead to enable the bead

interface to be in the same plane as that between sections 1 and 2. Typically with these

connectors, the frequency region around 8.7 GHz should be avoided since the connector bead

exhibits the characteristic to resonate over a very narrow band at this frequency.
APPROXIMATE FILL LEVEL

APPROXIMATE LOCATION OF

OPEN CIRCUIT, Ye = 0

PLANE OF MEASUREMENT

_ 14 mm REFERENCE PLANE

Figure 1. Cross section of open-circuit sample holder.

Figure 2. 14 mm open-circuit sample holders.
2.3 Theory of Electromagnetic Properties Determination

The sample holder is treated as a coaxial transmission line terminating in an open

circuit. The effective location of the open circuit is somewhat beyond the end of the center

conductor [4], as indicated in figure 1. The measurable quantity at the connector interface with the measuring instrument or at any transverse plane is the admittance, defined as

the ratio of longitudinal current to transverse voltage for the TEM mode of a coaxial line.

The admittance at the plane of measurement can be predicted theoretically by transforming

the admittance from the plane of the open circuit of section 1 to the bottom of section 3. The input admittance Yin of a section is

Yin = Yo

Yo + Ye cothyd

Ye + Yo cothyd (1)

where the TEM characteristic admittance Yo is

Yo

2Tr In b/a

o (2)

and

Y = /-wy^e^e* , the complex propagation constant in the section,

Ye = the admittance at the output end of the section,

d = length of the section under investigation,

a = inner conductor radius,

b = outer conductor radius,

= permittivity of free space,

e* = e'-je'', the complex relative dielectric constant of the dielectric

material in the section.

= magnetic permeability of free space,

CO = radian frequency.

It should be noted that both Yo and y depend upon the complex permittivity e* of the section.

Since there are three sections to the sample holder, eq. (1) is applied three times to transform the admittance from the plane of the open circuit of section 1, through section 2, and

finally, to the bottom of section 3 to obtain the theoretical admittance. The admittance at

a dielectric interface is continuous except when changes in radii a and b occur. Then the

shunt admittance of the step Y = iwC e* must be added. This is the case for section

step step

2.

*-'sj-ep> capacitance with air, is obtained from reference [5]. In theory, once calculated, sections 3 and 2 are known invariant sections whose admittances do not change with

the addition of an unknown dielectric in section 1.

To obtain the electromagnetic properties of dielectric constant and loss of an unknown

dielectric in section 1 from the measured admittance Ym, eq. (1) is used with Ye = 0 at the

plane of the effective open i.e., d = d^ + d' where d' is the added distance [4] beyond the

end of the center conductor to the effective open. With Ye =0, eq. (1) reduces to

Yin = Yo tanh yd . (3)

To solve eq. (3), the admittance value for Yin must be determined and is obtained from the

measured admittance Ym of section 3 by transforming Ym backward from the measurement plane

through the known invariant sections 3 and 2, using eq. (1), to the input of section 1. The

3
transformed admittance Y'm which is Ym transformed to the input of section 1, becomes the

admittance value required for Yin. Therefore, eq. (3) can now be solved and

Y'm = Yin = Yo tanh yd (4)

where the complex unknown dielectric e* appears both in Yo and in y- To find a solution, an estimate is given for e* in eq. (4), and iterated by Newton's method [6] until the equation

is satisfied. The equation has multiple roots but at low frequencies (100 MHz) with soil

dielectric, only the lowest root is reasonable. For higher frequencies, the previous low

frequency value for e* furnishes the first estimate for the Newton method.

To check that the theoretical admittance equation correctly characterized the sample

holder, the sample holder was measured with a known dielectric (air) in section 1. The

measured admittance Ym verified that all measured quantities, e.g., section lengths,

dielectric constants, Yo and Y were correct.

step

2.3.1 Center Conductor Correction For Electric Field Extension

To compensate for the center conductor with hemispherical end rather than flatly

truncated center conductor, a correction is required for d^ in eq. (4). The assumption

is made that the terminating capacitance [5] and the equivalent extension [4] is still just

the same as with the flat ended conductor. Therefore, a small quantity is subtracted from

the physical length d_^ of section 1. The amount subtracted is approximately 21 percent of

the radius of the center conductor. This method [3] was found to be valid experimentally

based upon measurement results of known materials e.g., air and carbon tetrachloride, when

measured using both a hemispherical and a flat ended center conductor.

The electric field which extends beyond the end of section 1 interacts with the

dielectric sample and contributes to the measured admittance Ym. This is correctly taken

into account in the above method. Not only does y contain e* but also the extended distance

d' in d was updated during the Newton iterations to be correct for the current value of e'. A correction for the loss e" was not used. More work is required to find the effect of e".

Finally, since the field extends beyond the end of the center conductor, a calculation

is required to determine how far the soil sample should extend. Theoretically, it should

extend to infinity. Practically, if the outer conductor is well below cutoff, i.e..

0.387V

bf (5)

where

f = the frequency in hertz,

b = outer conductor radius,

V = velocity of light with same units as length.

then the sample needs to extend beyond the center conductor at least a distance of 1.5 b. The evanescent field in the outer conductor decays as exp (-2.405 z/b) where z is the

distance beyond the end of the center conductor.

4
3. MEASUREMENT APPROACH

3.1 Measurement System

The electromagnetic properties (dielectric constant and attenuation) of the soil samples were obtained from the measured admittance as described in section 2.2. The admittance, in

turn, was obtained by measuring the input reflection coefficient V of the holder with its

sample at the plane of the connector (input of section 3) by an Automatic Network Analyzer

(ANA) . The ANA is a computerized microwave measurement system capable of making high-quality

measurements of complex scattering parameters at discrete frequencies up to 18 GHz. The ANA

calibration is conducted at the connector plane of interest (in this case, the 14 mm ref- erence plane) using high-precision short-circuit elements and a 50-Q sliding termination or

a high value return loss (greater than 50 dB) 50-fi termination. A large capacity computer

was used to reduce the measurement data to obtain mean and standard deviation values for

dielectric constant, loss tangent, attenuation and density.

3.2 Sample Preparation

Each soil sample was oven dried for approximately one hour at 120° C and at 10 minute

intervals until no weight difference could be detected. This procedure was used to establish

the dry soil weight condition of 0 percent moisture content. To achieve the various moisture

level conditions, the desired weight of distilled water was added and thoroughly mixed into

the dry weight sample. The moist sample was carefully packed into the open-circuit sample

holder by means of a nylon plunger. A hand held vibrator, placed at the base of the sample

holder, was helpful in packing the dry weight soil samples.

To help establish a higher degree of confidence in the results of the electromagnetic

measurements, three sample holders and like samples were prepared and measured for each

moisture level condition at each frequency. Results show that the standard deviation from

the mean value for density didn't vary between samples by more than a few hundredths gram/cc.

It should also be noted that there was less than 0.1 percent weight difference between the

initial and final weight measurements of the same sample.

3.2.1 Soil Texture Construction

The basic elements that are used in soil texture contruction are grains of sand, clay,

and silt which are defined as:

Sand - Washed quartz grains between diameters of 0.60 millimeters

and 0.027 millimeters;

Silt - Washed quartz grains (mica all right) between diameters of

0.021 millimeters and 0.0033 millimeters;

Clay - Inorganic clay such as Kaolin or Bentonite or a mixture of both,

such that plate diameters are below 0.0033 millimeters.

The five soil textural types as prepared by MERDC were described as being

constructed from the basic elements as follows:

Sand Texture - 9.5 parts sand, 0.5 parts clay, and 0.3 parts silt;

Sandy Loam - 6.4 parts sand, 3.6 parts clay, and 2.5 parts silt;

Silt Loam Texture - 2.0 parts sand, 8 parts clay, and 6.8 parts silt;

Clay Loam Texture - 3.2 parts sand, 6.8 parts clay, and 3.3 parts silt;

Clay Texture - 2.0 parts sand, 8 parts clay, and 2 parts silt.

Classification of the soil types according to particle size and distribution are illustrated on the soil textural triangle as shown in figure 3.

5
ure 3. Classification of each soil textural type on the

U

of Agriculture soil triangle. S . Department
4. EXPERIMENTAL RESULTS

Tables 1 thru 5 show the experimental results of mean value and standard deviation from

the mean value for density, relative dielectric constant, and attenuation obtained from

measurements made on samples of five different soil textural types as functions of frequency

and moisture content.

A plot of the magnitudes of relative dielectric constant e' and attenuation for silt

loam as a function of moisture content level and frequency is given in figure 4. This plot

is representative of the other four soil texture types and is given to show the shift in e' and attenuation that occurs with the higher moisture content levels starting at approximately

10 percent. Depending upon the soil textural type and moisture content, this shift or "window" seems to appear at approximately 800 MHz and levels off around 1400 MHz.

7
Table 1.

Experimental results of mean value and standard deviation (sd) from the

mean value for density, relative dielectric constant, and attenuation obtained

from measurements made on samples of sand texture for moisture levels of

0, 1, 2, 4, 8, and 14 percent.

Sand 0%

(Mean density = 1.540; sd = .022 g*/cc ) *gram/cubic centimeter

equency

MHz

Rel. Diel. Constant Attenuation - dB/cm

Mean sd Mean sd

300 2.702 .0486 -.00372 .0002

500 2.694 .0492 -.00206 .00006

1000 2.693 .0515 .00161 .0004

2000 2.695 .0515 .00833 .0003

4000 2.656 .0419 .0836 .004

9300 2.737 .0660 .240 .02

Sand - 1%

(Mean density = 1.614; sd = .014 g/cc )

Frequency Rel. Diel. Constant Attenuation - dB/cm

MHz Mean sd Mean sd

300 3.227 .0352 .0503 .001

500 3.131 .0299 .0680 .002

1000 3.062 .0182 ,0968 .0006

2000 3.015 .0112 .136 .001

4000 2.914 .0068 .304 .002

9300 3.037 .0132 .640 .05

8
^ Sand - 2%

* (Mean density = 1.455; sd = .015 g/cc

)

Frequency

MHz

300

500

1000

2000

4000

9300

Rel. Diel. Constant Attenuation - dB/cm

Mean

3.072

2.977

2.930

2.915

2.891

2.905

sd

.043

.032

.036

.079

.083

.038

Mean

0705

,0892

,113

139

,340

,789

sd

.002

.003

.003

.009

.02

.03

Sand - 4%

(Mean density = 1.583; sd = .020 g/cc)

Frequency Rel. Diel. Constant Attenuation - dB/cm

MHz Mean sd Mean sd

300 4.225 .168 .173 .01

500 4.079 .162 .197 .01

1000 4.019 .165 .231 .01

2000 3.940 .142 .287 .03

4000 3.946 .148 .607 .02

9300 3.373 .198 1.38 .32

*Note: The lower density probably caused the e' values to be lower than

those for sand-1%.

9
Sand - 8%

(Mean density = 1.732; sd = .016 g/cc )

Frequency

MHz

300

500

1000

2000

4000

9300

Rel. Diel. Constant Attenuation - dB/cm

Mean

6.957

6.792

6.708

6.533

6.425

5.854

sd

.235

.249

.300

.128

.196

.231

Mean

.249

.278

.335

.535

1.27

2.86

sd

.007

.01

.02

.02

.07

.18

Sand - 14%

(Mean density = 1.732; sd = .015 s/cc )

Frequency

MHz

300

500

1000

2000

4000

9300

Rel. Diel. Constant Attenuation - dB/cm

Mean

10.458

10.641

11.179

9.951

10.544

10.179

sd

.413

.415

.349

.334

.441

1.14

Mean

.251

.296

.429

.693

1.80

3.38

sd

.01

.01

.04

.05

.24

1.0

10
Table 2.

Experimental results of mean value and standard deviation (sd) from the

mean value for density, relative dielectric constant and attenuation obtained

from measurements made on samples of sandy loam texture for moisture levels

of 0, 1.5, 3, 6, 12, and 24 percent.

Sandy Loam - 0%

(Mean density = 1.435; sd = .008 g*/cc ) *gram/cubic centimeter

Frequency Rel. Diel. Constant Attenuation - dE/cm

MHz Mean sd Mean sd

300 2.650 .040 -.00195 .00008

500 2.642 .047 .00081 .0001

1000 2.660 .079 .00762 .0004

2000 2.680 .102 .00820 .002

4000 2.691 .125 .102 .01

9300 2.663 .027 .166 .09

Sandy Loam - 1.5%

(Mean density = 1.410; sd = .004 g/ cc )

Frequency

MHz

300

500

1000

2000

4000

9300

Rel. Diel. Constant Attenuation - dB/ cm Mean

3.791

3.548

3.341

3.243

3.023

3.236

sd

.008

.010

.020

.020

.034

.065

Mean

.124

.177

.277

.393

.743

1.58

sd

.001

.001

.004

.002

.02

.06

11
Sandy Loam - 3%

(Mean density = 1.402; sd = .022 g/ cc )

Frequency Rel. Dlel. Constant Attenuation - dB/cm

MHz Mean sd Mean sd

300 3.954 .067 .135 .004

500 3.690 .053 .194 .004

1000 3.464 .052 .308 .006

2000 3.278 .039 .412 .02

4000 3.174 .106 .798 .02

9300 3.190 .045 1.65 .08

Sandy Loam - 6%

(Mean density = 1.547; sd = .012 g/cc )

Frequency

MHz

300

500

1000

2000

4000

9300

Rel. Diel. Constant Attenuation - dB/cm

Mean

5.967

5.407

4.909

4.408

4.301

3.813

sd

.076

.062

.028

.035

.019

.084

Mean

.406

.520

.723

.913

1.43

3.42

sd

.005

.004

.01

.04

.06

.36

12
Sandy Loam - 12%

(Mean density = 1.650; sd = .044 g/ cc )

Frequency Rel. Diel. Constant Attenuation - dB/cm

MHz Mean sd Mean sd

300 10.063 .534 .985 .1

500 9.164 .681 1.16 .1

1000 7.759 .699 1.40 .2

2000 8.148 .555 2.33 .2

4000 7.551 1.294 3.14 .1

9300 "erroneous data"

Sandy Loam - 24%

(Mean density = 1.928; sd = .024 g/cc )

Rel. Diel. Constant Attenuation - dB/cm

MHz Mean sd Mean sd

300 24.527 .326 1.88 .002

500 24.328 .185 2.11 .002

1000 22.705 .625 2.71 .04

2000 21.156 1.072 3.51 .56

4000 16.549 1.56 4.27 .91

9300 9.884 2.4 9.57 2.5

13
Table 3

Experimantal results of mean value and standard deviation (sd) from the

mean value for density, relative dielectric constant and attenuation obtained

from measurements made on samples of silt loam texture for moisture levels of

0, 2.5, 5, and 10 percent.

Silt Loam - 0%

(Mean density = 1.106; sd = .037 g*/cc ) *gram/cubic centimeter

Frequency

MHz

300

500

1000

2000

4000

9300

Rel. Diel. Constant Attenuation - dB/cm

Mean

2.340

2.321

2.318

2.343

2.325

2.408

sd

.049

.051

.059

.085

.044

.094

Mean

.00325

.00771

.0188

.0351

.103

.188

sd

.0002

.0004

.0009

.003

.004

.019

Silt Loam - 2.5%

(Mean density = 1.133; sd = .043 g/cc )

Frequency

MHz

300

500

1000

2000

4000

9300

Rel. Diel. Constant Attenuation - dB/cm

Mean

3.137

2.959

2.812

2.728

2.646

2.660

sd

.029

.025

.018

.016

.018

.052

Mean

.102

.140

.205

.270

.519

.958

sd

.002

.002

.001

.005

.02

.04

14
Silt Loam - 5%

(Mean density = 1.267; sd = .017 g/cc )

Frequency Rel. Diel. Constant Attenuation - dB/cm

MHz Mean sd Mean sd

300 4.453 .097 .214 .007

500 4.038 .083 .301 .009

1000 3.692 .078 .467 .03

2000 3.391 .080 .589 .02

4000 3.319 .108 1.17 .10

9300 3.170 .092 2.30 .12

Silt Loam - 10%

(Mean density = 1.435; sd = .010 g/ cc )

Frequency

MHz

300

500

1000

2000

4000

9300

Rel. Diel. Constant Attenuation - dB/cm

Mean

9.151

8.083

7.458

5.573

5.275

4.065

sd

.186

.182

.343

.157

.048

.268

Mean

.675

.903

1.25

1.82

2.45

6.83

sd

.02

.04

.07

.10

.50

1.3

15
Table 4

Experimental results of mean value and standard deviation (sd) from the

mean value for density, relative dielectric constant, and attenuation obtained

from measurements made on samples of clay loam texture for moisture levels of

0, 1, 3, 6, 12, 24, and 48 percent.

Clay Loam - 0%

(Mean density = 1.266; sd = .035 g*/cc ) *gram/cubic centimeter

Frequency Rel. Diel. Constant Attenuation - dB/cm

MHz Mean sd Mean sd

300 2.775 .024 .00229 .00007

500 2.760 .027 .00625 .00006

1000 2.773 .037 .0167 .0002

2000 2.771 .051 .0289 .007

4000 2.758 .048 .185 .04

9300 2.708 .076 .404 .21

Clay Loam - 1%

(Mean density = 1.311; sd = .010 g/cc )

Frequency Rel. Diel. Constant Attenuation - dB/cm

MHz Mean sd Mean sd

300 3.265 .050 .074 .001

500 3.131 .048 .101 .001

1000 3.045 .041 .144 .001

2000 3.008 .037 .197 .009

4000 2.915 .064 .472 .04

9300 2.989 .141 .732 .03

16
Clay Loam - 3%

* (Mean density = 1.235; sd = .022 g/cc )

Frequency * Rel. Dlel. Constant Attenuation - dB/cm

MHz Mean sd Mean sd

300 3.402 .061 .123 .004

500 3.175 .056 .169 .005

1000 2.962 .066 .248 .01

2000 2.824 .100 .344 .02

4000 2.759 .055 .708 .06

9300 2.784 .048 1.29 .07

Clay Loam - 6%

(Mean density =1.436; sd = .035 g/ cc )

Frequency Rel. Diel. Constant Attenuation - dB/cm

MHz Mean sd Mean sd

300 5.667 .047 .283 .007

500 5.108 .023 .387 .007

1000 4.649 .101 .568 .003

2000 4.151 .065 .761 .06

4000 4.024 .156 1.14 .10

9300 3.826 .122 2.31 .73

*Note: The lower density probably caused the e' values to be lower

than those for clay loam-1%.

17
Clay Loam - 12%

(Mean density = 1.468; sd = .018 g/cc )

Frequency

MHz

300

500

1000

2000

4000

9300

Rel. Diel. ConstantMean

8.719

7.734

7.363

5.702

5.682

4.657

sd

.183

.138

.223

.018

.005

.418

Attenuation - dB/cm

Mean sd

. OOy . 02

.926 .03

1.43 .13

1.66 .08

2.26 .02

3.85 .68

Clay Loam - 24%

(Mean density = 1.920; sd = .021 g/cc)

Frequency

MHz

9300

Rel. Diel. Constant

Mean sd

14.283 ,324

Attenuation - dB/cm

Mean sd

15.46 2.32

Clay Loam - 48%

* (Density = 1.64 1 g/cc )

Frequency *Rel. Diel. Constant Attenuation

MHz , dB/cm

9300 9-75 38.95

*Note: The lower density probably caused the values for e' to be lower than that for clay loam-24%.

18
Table 5

Experimental results of mean value and standard deviation (sd) from the

mean value for density, relative dielectric constant and attenuation obtained

from measurements made on samples of clay texure for moisture levels of 0, 1,

3.5, 7, and 14 percent.

Clay - 0%

(Mean density = 1.174; sd = .040 g*/cc ) *gram/ cubic centimeter

Frequency Rel. Diel. Constant Attenuation - dB/cm

MHz Mean sd Mean sd

300 2.717 .052 .00455 .0003

500 2.703 .053 .00933 .0004

1000 2.721 .065 .0213 .0005

2000 2.721 .068 .0346 .008

4000 2.732 .105 .180 .02

9300 2.677 .052 .271 .03

Clay - 1%

(Mean density = 1.173; sd = .016 g/ cc )

Frequency Rel. Diel. Constant Attenuation - dB/cm

MHz Mean sd Mean sd

300 3.038 .022 .0782 .001

500 2.902 .023 .106 .002

1000 2.806 .032 .154 .006

2000 2.745 .049 .211 .009

4000 2.652 .034 .443 .05

9300 2.728 .185 .830 .09

19
Clay - 3.5%

(Mean density = 1.233; sd = .096 g/cc )

Frequency

MHz

300

500

1000

2000

4000

9300

Rel. Diel. Constant Attenuation - dB/cm

Mean

3.877

3.612

3.444

3.276

3.149

3.077

sd

.061

.050

.034

.039

.059

.179

Mean

.158

.216

.326

.385

.844

1.32

sd

.004

.005

.007

.02

.05

.27

Clay - 7%

(Mean density = 1.376; sd = .007 g/ cc )

Frequency

MHz

300

500

1000

2000

4000

9300

Rel. Diel, Constant Attenuation - dB/cm

Mean

6.030

5.399

4.952

4.187

4.289

3.754

sd

.034

.015

.058

.005

.085

.053

Mean

.334

.459

.702

.813

1.38

2.41

sd. .005

.005

.004

.03

.20

.43

Clay - 14%

(Mean density = 1.444; sd ,024 g/cc )

Frequency

MHz

300

500

1000

2000

4000

9300

Rel. Diel. Constant Attenuation - dB/cm

Mean

10.676

9.402

9.871

6.294

5.642

5.185

sd

.204

.186

.807

.124

.823

.950

Mean

.766

1.08

1.44

2.00

3.83

7.72

sd

.04

.06

.05

.08

1.2

2.5

20
.2 .6 1 1.4 1.8

FREQUENCY, GHz

Figure 4. Plot of the magnitudes of e' and attenuation of silt-loam

as a function of frequency and moisture content.

21
5. DATA SUMMARY

A few of the high-moisture content levels that were requested by MERDC could not be

furnished at this time. This included the moisture levels of 20 and 40 percent for the silt

loam (table 3), the moisture levels of 24 and 48 percent for the clay loam (table 4), and

the moisture levels of 28 and 56 percent for the clay (table 5). However, results for the

moisture levels of 24 and 48 percent for clay loam were obtained at 9.3 GHz and were included in table 4. These high-moisture level measurements were achieved by using a WR-90

rectangular-waveguide offset short-circuit sample holder. Similar high-moisture level measurements employing the WR-90 sample holder were also made on the silt loam and the clay,

but the results were found to be inconclusive. Two 14 mm short-circuit coaxial sample

holders were also used in our experiment to investigate the effects of the high moisture

levels on the three soil textural types at the lower frequencies down to 500 MHz. It was

found that verification of measurement results was difficult to achieve and were not

included in this report.

It should be emphasized that the values that were obtained for the relative dielectric

constant results in tables 1-5 are a function of sample density. In general, the larger the

sample density, the larger the value for relative dielectric constant. For example, see the

results for sand-1% and sand-2% in table 1.

6. CONCLUSIONS

A technique describing a three-section, open-circuit sample holder has been presented

that accurately obtains the electromagnetic dielectric properties of low-loss soil (< 20%

moisture level constant) by automated measurement techniques. Experimental results were obtained for five soil textural types that were measured in the open-circuit sample holders

as a function of frequency and moisture content. A few of the high moisture content levels

could not be achieved at this time because these are high-loss dielectric materials. The

main errors occur when the loss tangent is greater than zero, thus, allowing higher order

modes to be propagated. With the open-circuit sample holder, saturated dirt cannot be

accurately measured with the center conductor covered at frequencies above 3 to 4 GHz and

with high losses 1 to 2 GHz could be a limit.

However, the problem of high-loss dielectric materials could be solved if some effort

was devoted to a larger program that addressed this as one of the objectives. Future

experiments would include the gathering of a data base that would characterize the better

known soil types as a function of frequency, moisture content, and density. Sample holders

need to be studied and modified, and a proper mathematical model derived which is general

enough to properly describe the sample holder for accommodating high-loss dielectric

materials.

7 . ACKNOWLEDGMENT

The author wishes to thank Dr. Howard Bussey for his contribution to the section on theory of electromagnetic properties determination, to Mr. George Counas for his excellent

job in preparing and measuring the soil samples, and to Mr. Ron Wittmann for his role in

the data reduction.

8. REFERENCES

[1] Von Hippel, A. R. (Editor), Dielectric materials and applications, pp. 47-139, (John

Wiley & Sons, New York, 1954).

[2] Bussey, H. E. , Dielectric measurements of lunar soil, 1978 Lunar & Planetary Science IX,

Abstracts of Papers (Houston, Texas, March 1978).

[3] Jones, R. N., Bussey, H. E. , Little, W. E., and Metzker, R. F., Electrical characteristics

of corn, wheat, and soya in the 1-200 MHz range, NBSIR 78-897, (Oct. 1978).

[4] Somlo, P. I., The discontinuity capacitance and the effective position of a shielded

open circuit in a coaxial line, Proc. Inst. Radio and Elec. Eng., Australia 28^, No. 1,

7-9 (Jan. 1967).

[5] Whinnery, F. R. , Jamison, H. W. , and Robbins, T. E., Coaxial-line discontinuities,

Proc. I.R.E., 645-709 (Nov. 1944).

[6] Hildebrand, F. B., Introduction to Numerical Analysis, pp. 447-451, (McGraw-Hill,

New York, 1956)

.

22
NBS-114A (REV. 5-78)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 78-896

2, Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Dielectric Measurements of Five Different Soil Textural

X y LICo do X LLLXIm- uXl-' 11 S UX £ X «3U LLC LIV..' y CLllU. IVlW L o LVXX KZ \^ KJJ.LV^^LLU

5. Publication Date October 1978

6. Performing Organization Code

723

7. AUTHOR(S) T T 1. Ramon L. Jescn

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Taslc/Work Unit No. 7232417

11. Contract/Grant No. A7056

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

U.S. Army Mobility Equipment

Research and Development Center

Fort Belvoir, Virginia 22060

13. Type of Report & Period

Covered

Final

14« Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

Open-circuit coaxial transmission-line sample holders were used to determine

the electromagnetic dielectric properties of five soil texturell types as functions

of moisture level content and frequency, A brief outline of the theoretical basis

is given for the open-circuit method along with the measurement system and the

sample preparation, E.xperimental results are given for the different soil

textural types for moisture levels ranging from 0 to 48 percent and for test

frequencies ranging from 300 to 9300 MHz,

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

Attenuation; coaxial sample holder; density; dielectric properties; relative dielectric constant; soil textural types.

18. AVAILABILITY \^ Unlimited 19. SECURITY CLASS

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22. Price

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TirU^. Government Printing Office: 1978 - 677-072/1205